Cleaning and electroplating process



Patented May 25, 1948 2,442,195 CLEANING AND ELECTROPLATING PROCESSJames T. Clenny, Swampscott, General Electric Company,

New York Mass., assignor to a corporation of Nollrawing. ApplicationJuly 31, 1945, Serial No. 608,089

The present invention relates to the surface treatment of metal articleswith the object of removing adherent surface contaminations, includinginorganic material such as rust and scale, and also organic materialsuch as grease and oil. The cleaned surface, by a step in the sameprocess, is prepared by the electrolytic deposition of a metal whichwill facilitate the subsequent application by casting or otherwise of anunlike metal and thereby cause it to make a firm union with the cleanedand coated surface.

'My invention is applicable in particular to cleaning of metal castings,rolled plate, or forgings, and the subsequent application thereto of anunlike metal, for example Babbitt metal, to pro ducecomposite articles.My invention is particularly applicable to the manufacture of bearings.

'I-Ieretofore metal objects which were coated with oil or grease, andalso with rust or other oxides. have been subjected to a succession ofindependent stripping operations in order to remove such undesiredsurface contaminations. The cleaning operations in some cases werefollowered by an electrolytic treatment for depositing a coating metal.Commonly the cleaning operations included pickling in an aqueoussolution of a strong acid which is not desirable and is not suitable forcarrying out a plating operation.

In accordance with my invention I have provided a procedure comprisingthe combination of a plurality of electrolytic steps carried outsuccessively in a single fused electrolyte in which the metal object tobe cleaned functions alter nately as anode and cathode, As aconsequence, the treatment of the metal is simplified, short ened intime and made more efficient.

For example, in the course of manufacture of ferrous bearings forrotating machinery, it is required to remove adherent rust, scale andgrease, and it is desirable also that the cleaned metal surface nextshould be coated with a nonferrous metal which both protects the cleanedsurface of the ferrous metal from reoxidation and prompts alloyage witha non-ferrous metal.

These objects of my invention are attained by a combination of chemicaland electrochemical operations carried out in sequence in a fused alkalielectrolyte which may consist of a strong alkali, preferably causticsoda, having dissolved therein a suitable copper compound which isespecially adaptable to the manufacture or bearings, for example one toten per cent of copper oxide (CuO). However, oxides and metallic saltsof other oxidation-resisting non-ferrous metals 'may be used. Ingeneral, metals of the group 1 Claim. (Cl. 204-34) consisting of copper,nickel and silver can be used in a similar manner for variousapplications as protective coatings on metal surfaces.

The castings are immersed in such alkali bath which may be heated to atemperature in the range of 400 to 500 C. The articles to be treated areconnected to an electric circuit charged with direct current at apotential of about three to six volts, the polarity of the castingsfirst bein made positive. The negative cooperating electrode may beconstituted by the container for the electrolyte or by a suitably spacedelectrode which is connected to the negative terminal of the circuit.Theresulting passage ofcurrent causes oxidation and removal of thegrease and'other organic matter from the surface of themetal article.The anodic treatment is continued for only a short time. About oneminute is satis-- factory, the length of time not being critical. Thecurrent value may be about to 200 amperes per square foot of surface.

The polarity thereupon being cleaned becoming the cathode. The cathodictreatment is continued at approximately the same current density untiladherent scale and rust are removed. In general, about seven minutes issatisfactory.

The third step is carried out by reducing the voltage, and thereby thecurrent, to approximately one-tenth of the original density and bycharging the casting again to positive potential, that is, reversing thepolarity. By this step the spongy, loosely adherent copper which wasdeposited as an unavoidable incident during the previous step is causedto g0 into solution.

Finally, the metal article is charged negatively, that is, becomescathodic for the electrolytic action occurring in the fused bath. Duringthe fourth step, which is continued for about ten minutes, copper isdeposited as a homogeneous, adherent layer on the ferrous metal objectby electrolytic action, the current still being maintained at about 25amperes per square foot.

The ferrous metal object, upon the completion of the copper coatingstep, is removed from the fused bath and immersed in water. The waterdissolves the adherent coating of electrolyte. The surface of theferrous metal article upon removal from the fused bath is copper-coloredand retains this color after its immersion in water. The indications arethat the copper coating becomes alloyed with the surface of the ferrousmetal article.

the surface of the copper- As the final step, coated metal article iscoated with a suitable is reversed, the article flux, for example, aflux containing zinc and ammonium chlorides. The followin flux is il-Upon removal from the flux bath, the article is then coated with tin,eitherby being preferably immersed in a bath of molten tin or having themolten tin way.

applied in any otherconvenient tin; or 4 copper,

or no-s'egreg'ating of alloying constituents.

What- I claim as new and desire to secure by Letters Patent 01" theUnited States is:

The process of cleaning and copperplating the current through said baththe articleto the following series of electrolytic and article tosubject of alloys of copper, antimony and tin in the fol-5' JAMES T.CLENNY.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date. 1,004,673 Monnot Oct. 3, 191-11,417,896 Fletcher May 30, 1922 1,600,355 Otis et al Sept. 21,19261,795,512 Schmidt eta! Mar 10; 193 1 1,909,149 Hitner- May 16; 1933-2,042,800- Pike June 2, 1936 2,134,457 Tainton Oct, 25;,1938 2,311,139Tainton Feb.,16-,19,43; 2,327,676 Spence '24, 19.413 2,366,477 BayleyJan..v2,- 1.945 2,395,694 Spence et al Feb. '26; 1946 FOREIGN PATENTSNumber Country Date.

Great Britain, V Mar. 13,1935

